Hi.
I believe the formula for R when you have the voltage and current is:
V/I = R
Plugging in the numbers:
220/4 = 55
The answer is the second option, 55.
She could use the following methods:
8 dimes
16 nickles
2 quarter and 3 dimes
2 quarters and 6 nickles
so, 4 combos
The correct answer is C !